The invention relates to picture signal interpolation circuit, comprising:
means for receiving a picture signal encoded in accordance with a field skipping method, and
means for interpolating said picture signal to obtain interpolated fields between received fields of said picture signal.
A television system in which an original picture signal bandwidth is higher than a bandwidth of a transmission path is used, for example, in high-definition television for, inter alia broadcasting stations, in television conference systems, in television for monitoring purposes using telephone connections, etc. For picture signal storage, storage on discs or tapes having a more limited capacity is mentioned as an example.
A high-definition television system comprising in its decoding section a picture signal interpolation circuit as described in the preamble, is known from a discourse at a conference and an accompanying article entitled "TVDH 87", Ottawa (CA) 4-8 October 1987, vol. 1, P. Bernard et al.:"Analyse de structures de sousechantillonnage spatio-temporel d'un signal TVHD en vue de sa transmission dans un canal MAC" pp. 6.2.2-6.2.28". The introduction of high-definition television (HDTV) for domestic use is described for color television. Starting from the so-called MAC system (Multiplexed Analog Components) having its limited bandwidth, a compatible high-definition system (HD-MAC) is described. It is stated that there must be a balance between, on the one hand, the best HD-MAC picture available for specific receivers and, on the other hand, the capability of maintaining an acceptable quality for existing MAC receivers. To this end it has been proposed to use three picture signal channels with a shortest, an intermediary and a longest picture signal refreshing period, the shortest period being equal to 20 ms, in the encoding circuit and in the complementary, i.e., inversely operative decoding circuit. Dependent on the result of motion detection, one of the three channels is used locally in the picture. In the case of a motion of more than 2 pixels per frame period (20 ms) the channel having the shortest period is used. In the case of a motion between 2 and 0.5 pixels per frame period, the channel having the intermediary period is used and in the case of a motion over less than 0.5 pixel per frame period, the channel having the longest period is used. For obtaining the picture signal bandwidth reduction use is thus made of the split-up into sub-pictures which are stationary or which exhibit some motion or much motion.
In addition to the encoding operation which leads to the reduction of the bandwidth, it is well known to limit the bandwidth by means of the so-called field skipping method in which e.g. one of two successive fields is transmitted or stored each time. In this case the picture signal interpolation circuit operates with picture information from the previous and the subsequent field so as to form the non-stored or non-transmitted intermediate field by means of the interpolation.
In practice it appears that a non-optimum picture quality may occur during picture signal display when using the combination of encoding and field skipping. It appears that a troublesome area flickering may occur.